Why does the welfare system in capitalist countries cause brain drain and aging population?

The welfare system of capitalist countries (such as the United States) is more perfect than that of socialist countries (such as China), and the more subsidies everyone can get, which has caused a large number of foreigners to sneak into capitalist countries in order to obtain nationality. A large number of illegal immigrants have greatly squeezed American jobs. In order to retain immigrants, the governments of capitalist countries adopt preferential policies in employment, which further worsens the situation of domestic talents and forces them to leave their homes and live in foreign countries (but because foreign talents come to their own countries, they can get higher treatment and lower welfare). As for the aging population, let's take the United States as an example, not to mention that most people who go abroad to work are young and strong, and the elderly at home stay in the United States and continue to enjoy good welfare benefits. Even among immigrants, many are married with children, which naturally increases the proportion of the elderly in the United States to some extent.

The above views are personal and may lack comprehensiveness.